Dr No wannabes are finding that medium-priced islets were no great investment after all

CAVE CAY in the Bahamas, complete with beach huts, airstrips and breathtaking views, is going for $110m. Eilean an Seamraig, an uninhabitable Scottish isle featuring drizzle and rocks, costs a mere £45,000 ($71,000). The market for private islands has never been so unsteady, says Farhad Vladi, a Hamburg-based island broker with more than 120 isles from 22 countries on his books.

At the top end, the market is still firm. Luxury islands, which make up about a tenth of the market, have good access to food and water, few irksome bugs and a hospitable climate. Owners past and present include stars such as Johnny Depp, Celine Dion and Diana Ross. Demand for these islands is holding up, even in harsh economic times.

Elsewhere the story is different. Owners of so-called “adventure islands”—cheap, with fewer amenities—are ditching their retreats. Before the bust, prices soared as these places were seen as good investments. Mr Vladi says a Panamanian resort he sold for $100,000 in 2003 was given a price tag of $3m five years later. Now prices are declining. A densely wooded isle in Florida reckoned to be worth $1.6m before the crash sold for $260,000 in June.

Many islanders have wearied of the upkeep. Owning an island requires a lot of commitment, says Frits Hannenberg, who manages small island resorts for absent owners. Installing and running a water supply is tricky and costly. A desalination system costs up to $50,000 (you can buy an islet for that). Then the plants need looking after too. Locals can help, says Mr Hannenberg; in the Fiji archipelago, they are zealous at keeping the flora in order. But isle-buyers like solitude: Mel Gibson, an actor, gave up his after a row with tribesmen.

Other uncertainties include building rules and environmental hassles: islands (except when owned by villains in adventure films) are still subject to somebody else’s laws and taxes. Nicolas Cage, a film star, found he could not add developments to his refuge in the Bahamas, because an endangered iguana lived there; he has since sold up. A seller feared he would be unable to dispose of two Pennsylvanian islands, after one got flooded by a river. He gave them to charity. Climate change could mean sea-levels rising. That would put many island investments underwater.